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BIO 110 Dr. Ely Chapter 24.1 Notes – The Respiratory System I. II. III. Functions of the respiratory system a. Exchange gases with the blood i. Oxygen gas (O2) is inhaled into the lungs and diffuses into the blood ii. Carbon dioxide (CO2) diffuses out of the blood, into the lungs, and is exhaled b. Creates vocalizations for communication i. Vibrations of vocal cords in the larynx produce sounds Upper Respiratory Tract a. The nasal cavities are chambers within the nose to warm, filter, and humidify inhaled air i. The nostrils are the opening to the nasal cavities ii. Nasal cavities are lined with: 1. mucous membranes that secrete the fluid mucus in order to warm and humidify the inhaled air, and trap small particles 2. hairs that filter larger particles b. The pharynx (the back of your throat) connects the nasal cavity and mouth to the larynx; it is a common passageway for both food and air before they separate c. The larynx, or voice box, is supported by the hyoid bone and broad plates of cartilaginous tissue that prop it open. i. The glottis is the opening to the larynx. The epiglottis is a small flap of tissue that is pushed over the glottis when food is swallowed to prevent food from entering the respiratory system. ii. The vocal cords are flexible bands of tissue inside the larynx that vibrate to create sound Lower Respiratory Tract a. The trachea, or windpipe, is a stiffened tube connecting the larynx to the bronchi i. The trachea is held open by C-shaped cartilaginous rings that are flexible but supportive ii. The trachea divides into the right and left bronchi b. The primary bronchi (singular: bronchus) are two large tubes that continue to branch into smaller and smaller bronchioles. c. Bronchioles terminate in clusters of air-filled sacs called alveoli (singular: alveolus) i. The alveoli are the structures that exchange O2 and CO2 with blood capillaries ii. Their round shape greatly increases the surface area for exchange. iii. Exchange is also enhanced by the closeness of the thin capillary and the cells of the alveoli – creating a respiratory membrane that quickly exchanges gases 1. O2 – poor / CO2 – rich blood enters the respiratory membrane from the pulmonary arteriole (tiny artery) from the right ventricle of the heart 2. O2 diffuses into blood and CO2 diffuses out following their concentration gradients 3. O2 – rich and CO2 –poor blood leaves the capillary in the pulmonary venule (tiny vein) to return to the left atrium of the heart BIO 110 Dr. Ely iv. Emphysema is a condition, most often associated with smoking, which causes breakdown of the alveolar walls. This creates fewer, larger alveoli and thus less surface area for gas exchange. IV. Negative-pressure breathing a. Muscles involved with breathing i. The diaphragm is a muscular sheet of tissue that divides the upper thoracic cavity from the lower abdominal cavity. At rest, the diaphragm is curved upward. ii. The intercostal rib muscles are the muscles between the ribs that can contract to expand the chest. b. Inspiration (inhalation) i. The diaphragm contracts, moving downward. ii. The intercostals contract, which spreads out the ribs. iii. These two contractions serve to increase the volume of the thoracic cavity. This causes negative pressure, or a vacuum, that pulls air into your lungs. This is the opposite of pushing air into the lungs (positive-pressure breathing) like blowing up a balloon. c. Expiration (exhalation) i. The diaphragm relaxes, moving upward. ii. The intercostals relax, which brings the ribs closer together. iii. These actions serve to push air back out of the lungs as the thoracic cavity gets smaller. V. Breathing control a. The medulla oblongata in the brain stem monitors blood pH to regulate the breathing rate. i. If you hold your breath, the urge to breathe again is stimulated by a drop in blood pH. 1. CO2 is created by the cells and enters the blood where it mixes with water to form carbonic acid (H2CO3) which forms the hydrogen ion (H+) and the bicarbonate ion (HCO3-). The increase in hydrogen ion concentration lowers the blood pH. 2. In the lungs, the reaction runs backwards and CO2 leaves. But, if the breath is held, the blood grows steadily more acidic and the brain forces the muscle contractions that cause inspiration.